The present invention relates to fuel injection and intake air control apparatuses and methods for adjusting the amount of air introduced into a cylinder of an internal combustion engines, and more particularly, to apparatuses and methods for enhancing the starting ability of engines.
Electronic type fuel supplying apparatuses provided with a plurality of injectors to inject fuel into engines are known in the prior art. In a typical apparatus, the injectors are arranged in an intake passage communicated with each engine cylinder and located in the vicinity of a fuel chamber. The injectors inject fuel to the vicinity of the fuel chamber. The injected fuel amount is controlled in accordance with the running condition of the engine by adjusting the time period during which the injectors are opened. The fuel injected to the vicinity of the fuel chamber is readily drawn into combustion chambers. This improves engine performance, especially the responsiveness of the engine (the response in fuel injection amount) when the engine is in a transitional state. In addition, undesirable engine emissions are reduced.
However, the starting ability of the engine is less than desirable since the atomization of fuel is insufficient when starting the engine. To cope with this problem, the fuel injected from injectors is collided against the bodies of associated intake valves to atomize the fuel. However, it is difficult to atomize the fuel by colliding the fuel against the valve bodies when the surface temperature of the valve bodies is low. Furthermore, the velocity of the air flowing through the intake passage is low when starting the engine. Thus, it is difficult to guide the injected fuel using the air flow. This results in the fuel condensing on the walls of the intake passage and decreases the amount of fuel supplied to the combustion chambers.
Japanese Unexamined Utility Model Publication No. 1-119874 (first prior art example) discloses an apparatus that solves the above problems. The apparatus is provided with a control valve arranged in the intake passage to completely close the intake passage. The control valve is located upstream of the injectors in the intake passage. The control valve closes the intake passage to prevent a large amount of fuel from flowing into the combustion chambers during the period between when the engine is cranked until when the engine is started. The pressure in the intake passage at the downstream side of the control valve is decreased by the reciprocation of pistons so as to produce sufficient negative pressure. This increases the velocity of the air-fuel mixture that is supplied to the combustion chambers. As a result, the amount of fuel that condenses on the wall of the intake chamber decreases and the atomization of the fuel injected from the injectors is enhanced. Accordingly, the starting ability of the engine is improved. Furthermore, the amount of undesirable emissions (e.g., hydrocarbons) is reduced by the decrease in the amount of fuel that is required to start the engine.
Japanese Unexamined Patent Publication No. 63-235632 (second prior art example) discloses an apparatus that compensates for the amount of fuel injected from injectors when starting the engine in accordance with the coolant temperature. More specifically, when the coolant temperature is low, the amount of fuel injected from the injectors is increased. Application of this apparatus to the first prior art example hinders the supply of the optimum amount of fuel to the combustion chambers during starting of the engine. The amount of air-fuel mixture supplied to the combustion chambers and the amount of fuel that condenses on the wall of the intake passage changes in accordance with the level of the negative pressure. Accordingly, the amount of fuel injected from the injectors must be altered in accordance with the level of the negative pressure. Thus, it is difficult to inject the optimum amount of fuel into the combustion chambers during starting of the engine when compensating the fuel amount based on the coolant temperature. As a result, a large amount of hydrocarbons are emitted when starting the engine.
In addition, if the engine does not start within a short time after initiating cranking, it will be more difficult to start since fresh air is not entering the intake passage.